We have more power, we don't have to do what you say!
Under the Articles of Confederation, Congress didn't have the power to tax citizens of America. This was troubling because after the Revolutionary war, money was lost.
Congress couldn't enforce laws and treaties onto individual states, and the states had more power. If a person traveled into another state, they didn't follow that states laws if they did not want to. States also had their own currency that they used.
In 1786, a rebellion of poor farmers started called Shay's Rebellion. The state of Masachusetts taxed everyone within the state and the farmers went bankrupt. Angered, they statred protesting and got violent. However, the Articles did not allow a military, so a local militia had to difuse the situation. This showed how weak the Articles were, and that the government needed a change.